Various methods for applying coatings to a substrate are known in the art. One method of coating a substrate includes extrusion coating a substrate with a thermoplastic coating material. Such extrusion coated articles can be useful in a wide variety of applications, including, for example, as interior and exterior construction materials for homes, buildings, and furniture. According to this coating method, a substrate comprising wood, plastic, metal, or other desirable material, is passed through an extruder and a coating material is applied to at least a portion of the surface of the substrate. Once coated, the article is allowed to cool and the final coated substrate preferably exhibits enhanced aesthetic (e.g., gloss and surface smoothness) characteristics.
As the coated substrate exits the coating die and enters the cooling zone, water and other volatile material within the substrate may vaporize, thereby causing undesirable bubbles or blisters in the coating along the surface of the finished product. While at least partially submerging the coated substrate in a quench liquid has been found to help minimize this type of bubbling, quench cooling has also been observed to create a certain surface roughness that degrades the visual acceptability of the final product. Even substrates that show little or no blistering without a quench bath tend to exhibit undesirable surface texture when exposed to a quench liquid cooling bath.
Thus, a need exists for an extrusion coating process and system capable of producing coated substrates that exhibit an acceptable surface texture and appearance. It is also desirable that such a process and system could be economically implemented to existing extrusion coating systems, while minimizing process time and maximizing production rate.